Basic Operations

All the main parts USITT DMX512 (1990) (hereinafter, for brevity, we write simply DMX, if you do not mean others) described in "Data Structure" and "Physical basis of DMX512 (1990)" (which will be discussed in the next article) so here are limited to a small preamble. DMX protocol consists of a data stream that is sent to a symmetrical cable system from the transmitter (usually a console or computer) to the receiver (may be dimmer or any device described in the previous chapter). Single DMX port, transmitting data, is able to let through only information about a maximum of 512 channels. This port is called DMX domain (universe). For consoles, using more than 512 the number of channels, they need a second area (and hence the second port). See table 1 relevant areas and channels.

Restrictions on the number of areas there.

Remote Avolites Diamond II, for example, has six DMX512 areas and, accordingly, six DMX512 ports on the rear panel. It can control up to 512 x 6 = 3072 dimmers!

The only limiting factor, I think there is system performance. In this article we will examine the work of only the first area. Basic operation for different areas will be identical, except for the physical values of channel numbers. Must be remembered that the host device is physically able to recognize the channel number from 1 to 512. Thus, in systems with multiple domains, and technicians and artists, and operators need to compare the combination of region / channel when installing, connecting and programming the system. For example, a dimmer, which must be connected to the output channel 2331 console Avolites Diamond II, must be connected to the fifth area, and it will be spotted address 283. This is because the output channel 2331 is actually a 283 channel in the fifth area.

The data stream is sent as a package, which is constantly repeated. It consists of a start bit (which informs the recipient that the package is updated), followed by a stream of successive data frames containing the value of each channel from 1 to 512 or less (depending on the design and size of the controller). Each frame is separated from the other specific combination of start and stop bits. The whole system works as a city mail. Every postman (area) is 512 homes (channels). Each house (channel) has a personal address. Some houses - this high-rises with a large number of individual apartments (number of channels in one device). Postman goes from house to house and deliver a letter (disambiguation) in the mailboxes. Each resident only opens your mailbox and take only your mail. Likewise, each signal receiver has its own specific address and simply ignores all the data that are not directed to his address. In some devices the data is received for the initial address and multiple addresses after. Just as a security guard at the entrance, which receives all mail, and then distributes its tenants.

The data stream has a specific structure, which is described in the section "Data Structure", and the specific features that are described in the section "Physical basis of DMX512 (1990).